Field of the Invention
The present invention relates to a final controlling apparatus or control apparatus. More specifically, the present invention relates to a control apparatus used to control the flow of liquid or gas through a valve housing.
Control apparatuses with sealing means, particularly for sealing actuating spindles, are known, comprising stuffing boxes, O-rings, bellows, or also combinations of these. Thus, in particular to meet increased tightness requirements, e.g. in the use of environmentally harmful gases, control apparatuses are provided with double stuffing boxes or bellows seals with additional stuffing boxes as a security seal. Such control apparatuses are disclosed, for example, by G. Strohrmann in atp--Automatisierungstechnische Praxis 32 (1990) 10, part 1, pediatric patients. 479 to 488, and atp--Automatisierungstechnische Praxis 37 (1995) 7, part 1, pediatric patients. 22 to 41. It can also be learned from these references that in order to check the functioning of a bellows, or also the rinsing or drying (given chlorine) of the space around a bellows, given the use of at least two seals for an actuating spindle, a control terminal, also designated a warning terminal or revision terminal, can be arranged between the corresponding sealing locations.
Also known is the monitoring of the tightness by connecting gas sensors that are suited to detect the respective process medium. Gas sensors of this sort are often called "sniffers" in the professional jargon, and have the disadvantage that they can be used only for particular media, and their exchangeability is thus limited.
The reference EP 0 637 713 A1 discloses a device of this species for sealing an actuating spindle, in which a pressure sensor, for monitoring the tightness of a stuffing box, is used, by converting the measured pressure into an electrical signal and evaluating it in a downstream processor. A leakage that leads to a pressure buildup in a corresponding stuffing box can thereby be recognized using the pressure sensor and the processor.
However, the known monitoring of the tightness using such a pressure sensor has the disadvantage that all pressure changes, such as those arising for example due to temperature changes or due to piston movements of a bellows, and volume changes caused thereby, are misinterpreted as a possible lack of tightness. Since gas sensors are less sensitive to disturbances, i.e., temperature changes and piston movements during operation do not necessarily influence a gas sensor, they are generally preferred in practice to pressure sensors.
The outward sealing of a valve inner chamber, above all in the area of the actuating spindle, and the monitoring of the tightness are of increasing importance, particularly in connection with the technical manual Air (TA Luft).